The present invention relates to a method of producing a semiconductor device and, more particularly, to a method of producing a film carrier semiconductor device.
Generally, to produce a film carrier semiconductor device, use is made of a substrate in the form of a film made of polyimide, polyester, glass epoxy or similar insulating substance. The film is formed with sprocket holes for conveyance and positioning and a device hole for receiving an IC chip. Cu (cuprum) or similar metal loft is adhered to the film by an adhesive and then etched to form leads of desired configuration and pads for electric selection. Metal bumps in the form of projections are provided on electrode terminals formed on an IC chip. The leads of the film and the bumps of the IC chip are bonded together by inner lead bonding GLB) using thermocompression or eutectic. The resulting film carrier tape is subjected to electric selection and BT (Burn-in Test). Finally, the leads are cut off at a desired length to complete a semiconductor device. As for a multipin configuration having a number of leads, the tape or insulating film is often intentionally left at the outboard ends of outer leads in order to prevent the outer leads from being disfigured. Then, the outer leads are bonded to bonding pads formed on, e.g., a printed circuit board or an ordinary lead frame.
The film carrier semiconductor device has an advantage that the bonding speed is high because bonding can be completed at a time without regard to the number of leads. Another advantage is that the assembly including bonding and the electric selection can be easily automated for thereby enhancing quantity production.
The prerequisite with the above bonding of the film carrier semiconductor device is that a gang bonding jig applied with heat and load for the simultaneous bonding be uniform in heat distribution and be flat on its surface contacting the inner leads in order to insure a uniform load. Further, the bumps on the IC chip must have a minimum of irregularity in height while the inner leads of the film carrier tape must have a minimum of irregularity in thickness.
On the other hand, the contour size of IC chips is increasing in parallel with the advance of integration and functions. In fact, IC chips having as many as 300 to 600 electrodes are in development.
Although the conventional ILB scheme bonds a number of bumps and inner leads at a time without regard to the number of connecting points, the load required for a single electrode or connecting point remains the same. Therefore, the load required of the gang bonding jig increases in proportion to the number of pins; for example, assuming that a load of 0.1 kg is necessary for a single connecting point, then the jig must exert a load of 60 kg for a 600-pin IC chip. Moreover, the heat distribution of the gang bonding jig must be uniform even when the IC chip is sized (10 mm 15 mm).times.(10 mm to 15 mm); the temperature must lie in the range of from .+-.5.degree. C. to .+-.7.degree. C.
As stated above, to cope with the increasing size and the increasing number of pins of IC chips, the load for thermocompression must be increased, and the uniform temperature distribution and flatness of the gang bonding jig must be enhanced. These requirements highlight the following problems.
In the event of ILB, the load and heat concentrate only on several bumps to several ten bumps for a moment due to the short accuracy of bump configuration of an IC chip, particularly irregularity in thickness, and the short accuracy of the gang bonding jig and ILB device, particularly inclination or short flatness and parallelism. As a result, heavy stresses act on such particular bumps and cause nearby bumps to be short-circuited. In addition, the bumps peel off the interface between them and a silicon substrate or an insulating film, reducing the connection strength and destroying the chip itself. On the other hand, due to the short load and heat in the event of ILB, the bumps and inner leads peel off each other at their interface and lower the connection strength. This tendency becomes more prominent with an increase in the size of the IC chip and in the number of pins.
As stated above, the method which connects the bumps and leads at a time lowers the reliability of connection. It is therefore extremely difficult to increase the accuracy of the bump and lead configuration, particularly thickness, and the accuracy of parallelism, among others, of the gang bonding jig and ILB device due to the increasing size of an IC chip and the increasing number of pins.
In light of the above, there have been developed a method which connects a plurality of electrodes or bumps of an IC chip and a plurality of inner leads of a film carrier tape in a plurality of consecutive steps.
A single-point ILB method sequentially connects pairs of bumps and inner leads by use of a point bonding jig. An ILB device for practicing the single-point ILB method does not need complicated mechanical arrangements and is therefore miniature and low cost. Moreover, the point bonding jig needs only far smaller heat and far smaller load than the gang bonding jig because its contour is extremely small relative to the contour of an IC chip. For example, assume that an IC chip is sized 15 mm.times.15 mm, and that the tip of the point bonding chip is sized 0.1 mm.times.0.1 mm. Then, the heat distribution of the tip of the jig is less than .+-.1.degree. C., and the load necessary for the jig is only several ten grams to several hundred grams. In addition, the parallelism between the jig and the bumps of the chip can be readily adjusted.
However, the problem with the single-point ILB is that the temperature during the ILB procedure increases due to the increasing size of the IC chip and the increasing number of pins. As a result, the film carrier tape is deformed to lower the dimensional accuracy of the chip. Specifically, the single-point ILB connects the electrodes of the chip and the inner leads of the film carrier in a plurality of consecutive steps. Therefore, as the single-point ILB proceeds, heat necessary for ILB (about 250.degree. C. to 350.degree. C.) is transferred to the film carrier via the inner leads, sequentially elevating the temperature of the substrate or film. The resulting thermal expansion of the substrate causes the film carrier and inner leads to deform. Consequently, the electrodes of the chip and the inner leads are dislocated relative to each other, resulting in defective bonding and short connection strength.